[Baypiggies] Newbie-ish type questions...

Charles Merriam charles.merriam at gmail.com
Wed Apr 23 19:20:20 CEST 2008

Thanks for the help, saying I'm not crazy :)

Kelly:  I agree on letting duck-typing do its thing.  Most of the type
checking shows up in my testing code, along the lines of "I really did
get back a hash with values being an array of five arrays of strings".

Keith:  Unfortunately, the code is different for different tests of
types.  For example, "if type(l) is list" but if hasattr(i,
"__iter__")...  The use of function calls was to regularize the
interface.  The types module only defines nice words for the various
types, including things like 'code' or 'function' which take a couple
extra lines.  It doesn't simplify tests.

Paul:  I think you're right; at least it agrees with what I've read of
ABCs.  It means that all the tests of standard types become
is_instance tests.  Good.  It also looks like any arbitrary interface
can be described by overriding __instancecheck__.  Are there example
for "This takes an interface of (open(), read(), close()) so I return
true if you ask isInstance(ReadableFile)

Chad:  Thanks for mentioning the tests hiding in the operator class.
Just the thing I was searching for in the types module.   Ah, random

Paul:  FYI, also "strings" are sequences, "sets"  are not.

Thanks again,


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